If you were born in the '80s or later, you're at significantly higher risk of colon and rectal cancer — and experts say you should get screened younger

The American Cancer Society has issued new guidelines that suggest people should start getting screened for colon and rectal cancers at age 45 instead of 50.

The new guidelines were issued based on a disconcerting rise in rates of these types of cancers, known as colorectal cancers, among young people.

Someone born around 1990 is now four times as likely to develop rectal cancer as someone born around 1950, according to one analysis.

There are various types of screening tests that work.

Rates of colon and rectal cancers are rising quickly among young people — from 1991 to 2014, rectal cancer rates for people between the ages of 20 and 49 doubled. According to one analysis, someone born around 1990 is twice as likely to develop colon cancer as a person born in 1950, and four times as likely to develop rectal cancer.

This spike has led the American Cancer Society to recommend that people start getting screened for colorectal cancer, a term often used to describe colon and rectal cancers, at age 45 instead of 50, the agency announced Wednesday.

Colorectal cancer is the fourth most common type of cancer diagnosed in adults and the second leading cause of cancer deaths, behind only lung cancer.

For decades, colorectal cancer death rates for people 55 and older have been declining. That change has been attributed to healthy lifestyle changes and more widespread screening. But in recent years, rates of colon and especially rectal cancers have started to rise among a younger demographic. And researchers don't yet know why it's happening.

A search for explanations

It's worth noting that overall case numbers still aren't high for people aged 20 to 49 — rates in that group rose to 5.2 cases per 100,000 people from 2.6 per 100,000. But the change is disconcerting. The biggest increases have been seen in white Americans, who typically have lower rates of colorectal cancer than black Americans and some Native American groups.

As the ACS researchers explained in the paper announcing the new screening guidelines, the rise in cases of colon and rectal cancers cannot simply be explained by the fact that more cases are being found because screening is more common. People in this younger age range are not often screened, and death rates among young people are increasing too.

A study in the Journal of the National Cancer Institute discussing the changing disease rates noted that young people who are developing these cancers are in many ways healthier than they used to be. They drink and smoke less, but they have higher rates of obesity, which increases the risk for colorectal cancer.

The authors also think diet could play a role, with a Western-style high-fat, low-fiber diet increasing cancer risks. But there may be other not-yet-known explanations as well.

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Different types of screenings — it's not just a colonoscopy

Catching colorectal cancer early can make a big difference, since precancerous polyps — abnormal growths in the colon or rectum — can be removed. With early detection, these cancers have high cure rates.

But about one-third of people over 50 never get screened.

The ACS's new guidelines suggest that all healthy adults should start getting screened for colon and rectal cancers at age 45 instead of 50 and continue doing so through at least age 75. For people aged 76-85, the ACS says doctors and patients should decide on a case-by-case basis whether it makes sense to continue screening, based on life expectancy and preference. For people older than 86, the ACS discourages screening.

A screening for colon or rectal cancer isn't always a colonoscopy, though that is usually needed if another type of test indicates a problem.

There are six tests the ACS suggests as options for screening. Annual test options include two that can be done from home — for those, people collect a stool sample and send it in to be tested (the scientific names are a fecal immunochemical test and a high-sensitivity, guaiac-based fecal occult blood test).

Another option is a multitarget stool DNA test, which is done every three years and involves collecting a sample at home and sending it in. Every five years, a person could do a computed tomography colonography test (like a CAT scan) or a flexible sigmoidoscopy scan (essentially using a tube with a light and camera on it).

The ACS recommends a colonoscopy be done every 10 years.

The agency didn't recommend a specific test, saying a general recommendation for screening with different options is more likely to be followed.

The US Preventative Services Task Force, an independent expert panel that issues recommendations about preventative medical services like screenings, has previously found that there are strengths and weaknesses to different tests. But overall, getting screened using any of these tests reduces mortality rates from colon and rectal cancers when compared with not getting screened.

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Changing guidelines

According to the ACS, there's still a "strong recommendation" that adults begin screening at age 50. That wording means there's good evidence that doing so will help reduce mortality rates.

The suggestion that people start getting screened at 45 is what the ACS refers to as a "qualified recommendation." That means researchers still need more data on the effects of screening people at these ages to better understand how the practice affects colorectal cancer diagnoses and patients. But based on the ways colon and rectal cancers have started to affect younger people, the ACS determined that such a change is still important to recommend.

For now, the task force still strongly recommends people begin screening at age 50.

As younger patients get screened, there will be more data on how doing so affects rates of colon and rectal cancers. If the current trends continue, it's possible that some researchers could suggest starting screening at even younger ages.